code: def generate_obj_feature() -> Series:
      return Series(["a", "b", "a", "d", "d", "d", "c", np.nan, np.nan])
  
imports: import copy
  import numpy
  import pandas
  import pytest
  from pandas import DataFrame, Series
  from autogluon.common.features.feature_metadata import FeatureMetadata
  from autogluon.features.generators import AbstractFeatureGenerator
label_desc: Use image node_id 2 for calling the DataHelper obj's underlying member method code with example usage: obj.generate_obj_feature() and returns: Series